Electronic communication system



D. H. RANSOM ELECTRONIC COMMUNICATION SYSTEM May 9, 1950 5 Sheets-Sheet 1 Filed Jan. 25, 1946 A TTOPNEV May 9, 1950 D. H. RANSOM 2,506,612

ELECTRONIC COMMUNICATION SYSTEM Filed Jan. 25, 1946 3 Sheets-Sheet 2 VI BRATOR l0 K.C.

' |34 `|35 w E; L74 $7 se se L//VE F//VDE/P 11 SPEECH @L i HN PUT GATE SPEECH OUT PUT GATE 79 T F l G 2 DAWD gyllrsgom A TTOR/VEV May 9, 1950 D. I-I. RANSOM 2,506,612

ELECTRONTC COMMUNICATION SYSTEM Filed Jan. 25, 1946' 5 Sheets-Sheet 3 COUNTER ILL] I Iza-T l A" 'i LAsT |02 LAsT REGISTER TIME CHANNEL COUNTER IN V EN TOR.

REG/STER/NG 8 L//VE SELECT/NG EQU/PMENT DAVID H. RANSOM f FIG. 3 BY A TTORNL/ Patented May 9, 1950 .ELECTRONIC COMMUNICATION SYSTEM David H. Ransom, Montclair, N. J., fassgnor to Federal Telecommunication Laboratories Inc.,

:New York, N. Y., a, corporationof Delaware 'Application'.lanuary 25, 1946,.'Serial N0..'643;,285

kk(Cl. 179-18) 16 Claims.

.The invention relates to newr and useful improvements in .commu-nication systems .and

...particularly .in telephonesystemsof the type .dis- .closed in the copendingapplication ofE-M-Deloraine, Serial No.. 628,613, filed November 1f-i, 1945. The..object of .the invention .is an intercommu nication system in which, through .the Cagency :solelyiof electronic. means -(vacuum tubes, cathode ray tubes and atheli'ue.) :and Without empio* ing any electromechanical devices CrelaysV step- 'by-stepf switches 4and the like) .twoawaycommw .nication can be established vbetween l,calling .and `called lines.

According 'to the. present invention,..this .object is attained by `providing A:signal le;` .g'., 1speech) input .and outputgate-tubes. .Theinputgate is operated under .the .controlof .either .thecalling or the :called -line-to loperate the youtput..gate which.. in turn, canappl-y thesignals to eitherthe calling or the-calledlline.

Preferably, `the input. .and .output .gates .are pentodes to Whosei suppressor grid .a r.potential is applied only -during .-timeehannels whenthe .calling vand vcalled lines areconnected with lthesystem, to open the.gates'.only-duringthese'brief periods.

-These .and yother obj ectsof .the .invention .will more clearly .appear from vthe `epi-)ended claims and from the.detaileddescription oan .embodiment of the invention-Which..isdiagrammatically illustrate-d in the drawings.

En readingthe drawings., Fig.'l lshouldbe placed on top Yofligs. Zand 3, .the..latter b,eing .=p1aced side by side. 'The upper leftl-liand=.corner.ofiFig. 1 diagrammaticallyy illustrates equipment at Xsubscribers.stations.andtheloalance of the drawings diagrammatically .illustrate `eduiprnent acentral office. Only so rnuclfi isfshown asisnecessary for a. clear .understanding o'tltheinventicn.

The telephone systcnm. here. .exemplified .com-

. prises a y.pluralityof -subscribers .,VlineS,` twenty for .ex-ample,..to .which .are assigned numerals. l to .each of .these .lineshaving substation equipment .such .as'.21,I allishown in lthelef-tehand cornerof. l. .The otherequipmentto thaleit of the dotted-f-line -inLEig... l .is .common .toallthe line circuits. VThe sy'stem'further comprises-.a

. group.oilinkcircuitacnc of which is ,needed/for 'deiity for..spe`ech. transmission.' 'The base frequency is .derived .from ai 2il0-.l;iloeycl e .stable `oscillator preferablycrystal. controlled;r bejcause it yis easier .to build .a .stable voscillator at "3H -and a ,normally 'open switch hook 3|.

2 the higher frequencies than in the v10,000-cyc1e frequency range. The .sinusoidal lfrecniency Agenerated in master oscillator 23 is reduced to the A.base frequency vof ten kilocycles vin frequency divider The output of frequency divider 124i isapplied .over ,96 phaseshiiter 2:5 to .the vertical andhori- .,.zontal .sets fof .deiiectiue plates of distributor .tube22- This .will serve. to rotate the Abearnof tube V22 Aat ya .frequency of 10,000 revolutions per second .so tlia.t...e.21.cl'1of thedynodes of the tube Will be scanned once.every 10,'000ths of a secQnd. 'Incoming linesy Iv, .5 and '2 are shown connected todynodes '2 6, 2l .and 28.

.At 2l is illustrated a typical subscribers .set (shown connected to line 5) comprising a voice transmitter'ZS .connected .in series with a dial The .receiver 3 2 is. bridged .permanently across the line, since, 'forthe sakeof simplicityno separate ringing .equipment is shown. The signal for sum- .moning a Kcalled subscriber may be applied `as .a special tone' which will "be reproduced :in receiver. 32.

"' Upon initiatingacall, theswitch 3l is 'c losed,

.completinga circuit inthe callingline loop over low pass iilterj vand the associated .linesat the sub-set, .applying negative potential .from ,battery ed to ythe associated dynodeZ'l. "Normally,

thezdynode electrodesareatthe same potential as anode't and no current flows. Thisnegative potential Will produce apotential difference .and

cause secondary .emission current to flow from thev dynodes .uponinipingement of thebeam .of tubeZZ thereon, producinga negative output pulse to furnish .energy for establishing and maintaining.. connections regardless of modulating signals. "The negativepulses resulting from the .operation of theselecteddynodel'l arefed to the gridof cathode follower and inverter tubejl. The anode circuit of tube 38 is coupledto the grid of clipper .tube' Which s ervespto clip the pulses im ata predetermined level so as topass only the modulated .portions thereof. .Thus, the output of this tube, v.repr.csentirng the speechsignals, may be substantially '166%...modulated The clipped pulses Ml `.are then .applied Ato a, cathode follower jtube 4l and' .from thereto all, of the link circuits over ...the Outplitlead 42.

Asecond. outputis taken acrossthe cathode resistance ofinvertergtube 38 and thefpulses are apvpliedto a clippergtube .4,4 Whichserves to clip the pulses .43 to .a constant level, eliminating modulation veiects. `therefrom. This tube is. biased to draw current normally sc that each negative pulse L43 .will drive it beyond cutol, clipping any .,Wliichserves toY apply pulses 45 through common 'feed resist-or Hand loyerwired to thevgrid ofline an integrating network B1.

'applied to the grid thereof overv line 1|. amplied wave is then passed through phase in bias of tube 51. 159 and 92 is roughly constant, While the value of finder gate tube 49 (Fig. 2) inthe rst link circuit (now under consideration), and in parallel to the grids of the corresponding line nder gate tubes f in all other links. Y

The pulse 46 after passing through resistor 41 may be designated 59 which arrives at the-grid of tube 49 and the other line finder gate tubes. Under the conditions now assumed, when none of the grids of the line finder gate tubes is drawingV normally operating at a frequency slightly lower than the output frequency from frequency divider 24 in Fig. 1. Oscillator 5| may have, for example, an ouput frequency of 50 kc. which is applied as rectangular selecting pulses 53 through a clipper amplifier and differentiating circuit 52 to a multii vibrator 54 arranged to synchronize at 10 kc.

The output of multi-vibrator 54 is applied through a diierentiating net 55 and 56 to the control-grid of clipper tube 51 in the form of pulses 58. Tube 51 is normally biased beyond cut-off but the leading edge of each square wave output 59 from multi-vibrator 54 is` of suicient strength to drive the grid positive on a portion of the square Wave. The trailing edge of pulse 59 is suppressed. A negative pulse 69 of approximately iive microseconds is produced in the plate circuit of tube 51. A cathode follower tube 6|l passes the negative signal or control pulse 52 to the cathode of line finder gate tube 49.- The frequency of the linev f finder lock-in oscillator 5| being slightly less .thanthat of the master oscillator 23, the pulses 59Y and 62 will drift in time. When the signal 59 on the grid of tube 49 coincides with the selecting pulse i 2 to the line selecting circuit.

The pulse 63 is rectified in tube 64 and fed to The negative potential from the integrator is amplified in tube 68, reducing the potential in cathode resistor 69 which is common to tubes 68 and 19. The reduction of this potential renders tube 98 conductive, and tube 19 will now commence to pass the sine wave from master oscillator 23, which is continuously corrector circuit 12 serving to lock-in oscillator 5| with the master oscillator 23.

A portion of the rectied output of diode 64 is fed tc a control grid of delay gain control tube 13.

Operation of tube 13 increases the positive voltage on the screen of clippertube 51 increasing the amplitude of the output pulses E9 and hence B2. The value of resistor 41 and the grid current .characteristics of line nder gate tube 49 are such that the total positive swing of its grid with respect gto `its cathode cannot exceed a predetermined small amplitude regardless of the magnitudes of pulses Scand 92 which are applied, respectively,

to the cathode and Via resistor 41 t0 the grid of tube Y49. However, the square pulses 92 from tube 8| will increase in amplitude with the change This t v mally conducting) The decrease in pulse 59 does not, however, reduce the response of tube 49 in the rst link (now under consideration) since the total input between grid and cathode is not decreased. Thus, pulses 63 of roughly constant amplitude are applied over line 14 to gate control tube 18 which serves to control the suppressor bias on the input gate tube 11, and in multiple to the grid of control tube 19 of output gate tube 89.

The speech input gate tube 11 is normally conditioned by suppressor grid bias so that the pulses applied thereto from the output of cathode follower 4| over line 42 will not be passed. However, upon operation of tube 16, by selection of a predetermined incoming line as described above, the potential on the suppressor grid of tube 11 will make the tube conductive during instants corresponding to a certain time channel. Combined dial-and-speech pulses will, therefore, be sent from the outputv of tube 11 over line 8| (Figs. 3 and l) to the pulse stretcher 82.

The line finder having now operated, the pulses corresponding to theA time channel individual to the calling line thus applied to pulse stretcher and integrating network 82 are amplied in tube 83 and applied over transformer 84 to the control grid of clipper tube 85 and over a second pulse stretcher and integrating net 89 to the control grid of a tube 81. The integrating network 82 in the input circuit of tube 83 functions as a low-pass lter whichvwill pass the dial pulses but will not pass the higher frequency communication signals. The clipper 85 serves to shape and clip the incoming dial pulses to form square wave pulses which in turn are differentiated in net- .work 88 and applied to the control grid of dial gate tube 89. Tube 89 is biased so as to suppress the negative part of the differentiated pulse, corresponding to the leading edge of the square dial pulse, and to pass to the register circuit only the positive part of the differentiated pulse, corresponding to the trailing edge of such square wave pulse.

Dial gate tube 89 is normally biased to conduction by the-voltage on its suppressor from the dial gate control tubes 9|, 92 (with tube 9| nor- Tube 81 cuts oif at the beginning of a series of dia1 pulses (sending out an ineffective positive pulse) and re-operates at the end, sending out, through 93, a negative pulse to the dial gate control 9|, 92. The negative pulse from tube 93 cuts oi tube 9| causing tube 92 to conduct. This biases tube 89 to cut-off, locking out the dial gate s0 that transients and Voice modulations, or even additional dialing will not disturb the registers. At the same time, a control Voltage is sent out over lead 94 biasing the con- Thus, since the sum of pulses i the component 52 is risingthe magnitude of f to prevent other line finder lgatetubes (similar to 49 but in other links) from responding.

trol grid of the output gate 89 (Fig. 2) for conduction.

In other words, the leading edge of the first pulse in the output circuit of the pulse stretcher and integrating net will cause the flip-flop circuitcom-prising tubes 81 and 93 to transfer conduction, from 93 to 81. This condition will be maintained throughout the series of pulses on the grid of 93 by the potential build-up in the low pass filter 18. At the end of the series, 93 will again resume conduction, sending a negative pulse to the gate control tubes 9| and 92. Normally, 9| is conducting, biasing the suppressor grid of the dial gate tube 89 to pass signals, and

the control grid Vof the output gate tube 89 to cutoif. The negative pulse at the end of a series of pulses transfers conduction from 9| to 92, and closes the dial gate 89 so that transients will not change the register settings. The output gate 80 vwill be A'openedfto *permit the passageof and' lll2 to Vcut-offy on lthe'irassociatedi suppressor 1 f 'grids- `When1a series df dial'pulses h-as'beenreceiVed, oneof'the'ri'ghtehand tubes of the register Will 'be left conducting, .permitting its g'ate`t1;1.b`eto .pass the signal.

Theirst 'trigger circuit "has no IVassociated gate, rand tubel?, `isnorrnally conducting.' A first pulse over Wire 95`fr'om the pulse forming circuit `cuts' off Stube l'l- 'of 'trigger 4'circui-tSl, causing'tube' HM v'to conduct. 'Anegativepnlse is now sent from the v:plate .circuit ofl D# to tliegrid of the' normally conducting tube T195' of trigger circuit 91,'cuttingroff'fthis'tube and causing tube list fto conduct: This foperationof tube i196 serves -to openthe firstg'atetub'elfll. Y

The second negativepulseL-from thepulseforml:

ing circuit cuts 01T- tube' V05" transferring conduction' to :tube t El 5. A negative pulsefrornfthe" plate 0f tube'il' 'cuts oiTtube `l0'l"restoring gat'el'a to blocked condition fwliich 'transfersfconduction ftotube 'l [i8 .in the "#2 register. The :conduction kofV4 tube l'il unblocks theisecond gateitube'il'."

- cycle is repeated'in "succeeding registers 'until the 'last dial pulse hasbeen sent.

Thus; at the end of dialngzonlythe gatecorreblocked.' Assuming that line 3 Ais callingrline, the secondi-gate lill vwill .loel unblocked. .l-dises which .may "arriveonthe :grids 1 of'y the.- gateftubes ite; g.V over-lines' lisi vl'll,"'et'c;) will'befpassed only "by: gate il lll 'to theiconimoni output wirefl l' l.`

The"dial'ofeachlineis set!y so that number /ofpulses'corresponding tothediierence between the calling line and the called line will be .transrmitted. It` thus 'becomes' 4"necessary to produce time'di'splacementsinthe'communieation energy corresponding tothe' :difference 'inf timing between thescanriing'of the two'lin'es'linthefeathodefray scanning device '2 21' The "differentv signaling pulses operate 'through the pulsieiregister 'circuit' as idescribed "above, 'to :select the'rdesirediti'rne fdisplacef kment ,in accordancewith theficalledrline.

Instead" of 'producing a truetran'smission:delay in"'the 4signals from "the calling Jline., V:these fare Istored'and then .later released. vTo'determine vthe proper'inst'ant for releasing thestored sigf;

nais, the equipment '1r 'counts the pulses which mark the time :channels inte'rveningfbetweenfthe calling and called line ichannels. f

In vorder to 'start Athe 'counting 'at'thefinstant corresponding to fthe' calling lines 4-time' channel, ,i

a synchronizing 'puls'e'ffrom f the :line nderzrgate tube VIlSl-over'line SS vand-.line fl |22 isipassed through the pulse shaping amplifier H3 to thexs-ynzlhro- -nizing counter Mil. -'-We`;netethatf1f" 3: is. conl2! of all the'countersfrare :conducting: 'The'.'syn- .chronizing pulse it?? l'applied tothe'` gridloi? rl'l flips Vconduction',in the-0 counter f1'cm'tube-ii'5rto tubellf,

lllegative .impulsesY are vsent at 5' :as fintervals from the `master oscillatori'over' conduetortll and the shaping ampliier'fl25, andfaleppledfcas ypulses l2@ to the grids of :allithelrght1hand=tu1ees f llinef-Asthe countersAv operate successively, they applyipotentialsf to' Wires |09, lll), etc. But, if `only-gate lll'l is fonenonly thepotential on wire -l`lfl3z will ipassltol common wire l l l,V thus properly timinfg'the 'release of speech'sig'nals to the'called Vline'as-vvillshortlyappear; f

The incoming energy'from lthe speecl'rinput gatei-tube i'llfisapplied by meansoia low pass lterllfand'J-audio famplieril-Zfl which serves 'as-a 'storageimeans -for ther-incoming speechfsignals. These speech-signals from the output of lter lf2-l Aare Continuously applied 'to `the fcontrol 'grid of speech outpulfgateitube'll; However, nef-energy #can passvlun'tl thecompletion of dialing when'the icutofbias i's removed fromcontrol grid of' gate time las #thei properffgate -pulses yare applied from vvir-e Tlil l -foverfWir'e l 28 Vto-cutoff gate vcontrol/cubes landl 'lywhic'hinturn'remeve the biasl on the suppressorfgii'dsoftubes fand-Bil. IThe biasi will beA removed' atl the fproper time dependingr upon the time channel gate lim- |32 which happens v.tube open'. Y

' "ILQOrReiampla lthe #Si lregister is `conducting vioni its lright-handtube Tlf, then the positive bias ti-me'fchannelgate tubeflfllil so that ywhen the #l .counteriflipsfconduction 'to the right-hand tube i8; la "neg-ative; signal will bey Ygenerated Von the -iplatefof -lll'f and 'passed over wires "l l l and -l 2 tio-1 th'egate control' ltubes Y and?! 9.

The following circuit is nc'wreadyftopass the Speech Fsignal z ifrornlthe eclyn'od'e l2l of line 5 (Fig. 1) to the cathode follower and inverter 3S, clipper .tube' 39,;c'athod'e follower 'tube lil, conducto-rez, .tolti-1e controlgrid-of the inputgate-tube 'l'l' (Fig. 22).'` Itliwillbe remernb'eredbthatfthe input gate itubefllfisfopenediby apuls'e 'frornthe plate of the -lineinderzgatehlivia vcontrol tube 'l-S whereby onlywheuaulse initiated the-calling line is permittedtoepass. 1 L'Thesigna'l from the plateof input gate 'li-is ifeditothelowpass:lter l'ZlWhere it is converted tofth-eoriginalspeech:signal and passed-onto the control grid of the speech outputgatells This rgaterisfopehed byzthetsignal .from the lline selecetorcirnuitf'liii'g-f3) Lseritab'ythe time channel' gate lie fcveifconductor'fistrand@corresponding `to the time period of the called line.-'Arnedulated-pulse may thus be transmitted from thelplate-of output ztoitlfie'z-'gridtl 31er. .thedistribntingtube '122. At the finstani:;,when;the"b'e`am sweeps'theicalled line, the

Jsignal .bispas'sed through 'the flow `filter (core -respondingitof-l @tol-the 'subset of the called kline. Thefcalling subscriber-signals 'at voiceV frequency. Tf'When-theeallfis lanswered,'fslreecli in the' oppo- :site L'Hirection lfpasses through "exactly `the Vvsame p'ath, the-lonlydiifer'ence being that-now ythe timingsoffitheiiinputffgateTfl-'lv isfunderf the *control of theflne selecting circuit'iconductor t2 8=being mul- I,has no effect.

. call.

1#spied to the grids of both gacontroitubes 1s Aand 19), and the output gate 30 is under the control of the line nder circuit (conductor 'Mbeing also multipled to the grids of both gate control tubes and '19).V

jhappens to be operated is fed over conductor Il I vand a pulse-shaping amplifier |3| to the gridv of Aa busy gate tube |32. This will produce a negative pulse on conductor 48 which will neutralize the line pulse 58 that would otherwise be prov'duced on this conductor by the initiation of a call. A line finder gate corresponding to 49 cannot, therefore, be operated.

When the calling subscriber hangs up at the end of the conversation, the various circuits are released under the control of the delay gain tube 13 (Fig. 2). The register and dial gates which are locked-in are released by the release tubes I 33, |34 and |35 in the following manner:

When the call is initiated, the delay gain tube V'I3 is driven to cut-off, thus lowering the potential on the grid of tube 34 connected with the cathode of tube 13. This causes the conventional ipvilop circuit shown to transfer conduction to tube 33 whereupon a negative pulse is sent to the grid Iof tube |35. Tube |35 is biased beyond cut-01T and the application of a negative pulse to its gri When the line finder releases, tubeA |34 again This positive multipled to the various registers transmits the signal to the gate control tubes 9| and 92 and re- Y l.stores them to normal. i

The circuit is now in condition for the next The delay count may be started from a fixed Ireference instead of from the line finder pulse. This permits the installation of the same dials Iat all the stations and the arrangement ofthe central oflice equipment for multi-digit operation. For this purpose, the zero terminal 26 Vof the distributor 22 is made inoperative and the ,pulse shaping amplifier ||3 (Fig. 3) is disconf-nected from conductor 8| and connected with conductor |38 and, thus, with the frequency di- ,vider 24 of Fig. 1.

Otherwise the circuits are left unchanged but 7 the assigned number will be dialed, and the time count will start from the Zero timechannel in- Istead of the line finder pulse.

WhatIClaim is: -f l. In a communication system, a plurality of lines, an electronic means common to said lines `effectively associating the input circuit with the electrodes of the calling and called lines when fthey are swept by the beam, means for eifectlvely ,associating the output circuit with the control grid when the beam sweeps the electrodes of the calling and called line, and timing means Yfor applying to the repeater signals originating on calling and called lines when the beam of said electronic means sweeps over their terminals.

2. In a communication system, a, plurality of lines, an electronic means common to said lines and having a plurality of electrodes in which the lines terminate, a control grid and means for cyclically sweeping the electrodes with an electron beam, a plurality of signal repeaters each having an output connected with said control grid means operative upon the initiating of a call for taking into use one of said repeaters, timing rmeans for applying to the repeater signals originating on calling and called lines when the beam of said electronic means sweeps over their terminals and means for releasing the repeater taken into use by the termination of the call.

3. In a communication system, a plurality of lines, electronic means having means for moving a beam of electrons, a control grid for the vbeam and a plurality of electrodes in which said lines terminate, vmeans for operating said electronic means continuously and cyclically to sweep said terminals with its beam, a plurality of signal input and signal output tubes provided in pairs, means operative upon the initiation of a call on a line for selecting a pair of tubes, input, output and control circuits for the selected tubes, means for operating the controlV circuits to render the selected pair effective when the beam sweeps the electrodes in which the calling and called lines terminate and ineffective at all other times, a connection from the output of the input tube to the input of the output tube, means for asso- .,ciating the input of the input tube with the electrodes in which the calling and called lines terminate when they are swept by the beam, and means for connecting the output of the output tube with the control grid when the electrodes of the calling and called lines are swept by the beam. Y

4. The system according to claim 3, and in Awhich the input and output tubes have cathodes, .,anodes, control grids and suppressor grids.

5. The system according to claim 3, and in which the input and output tubes are pentodes.

6. The system according to claim 3, in which the means for selecting a pair of tubes comprises a normally inactive line finder gate tube, means vfor actuating said line finder gate tube upon the initiation of a call, and means for operating the last-mentioned tube to convey signals from' the calling and called lines to the signal input tube whenever the electron beam sweeps over the terminating electrodes thereof.

7. The system according to claim 3, and a low pass filter in the output circuit of the input tube.

8. The system according to claim 3, and means in the output circuit of the output tube to keep the total gain around the system at less than unity.

9. A system for. interconnecting two channels of diferenttime displacement for two-way en- ;ergy transfer between said channels, comprising Va rst means for receiving energy from either channel,-a second means for applying energy to either channel, means for transferring energy from said first to the second means, selectively -operable Vmeans common to said channels for vproducing a time displacement of the energy received from one channel equal to the difference in time displacement between said channels, line ,finder means common to said channels and responsive to energy received from a channel, and means jointly lcontrolled by said line finder and selectively-operable means for operating said first means under the alternate control of both channels.

10. The system according to claim 9, and in which said first and second means are normally ineffective vacuum tubes, and means jointly controlled by the line finder and selectively operable means for alternately rendering said tubes effective.

11. A system for interconnecting two channels of diierent time displacement for two-way energy transfer between said channels, comprising a rst means for receiving energy from either channel, a second means for applying energy to either channel, means for transferring energy from said first to the second means, selectively operable means common to said channels for producing a time displacement of the energy received from one channel equal to the difference in time displacement between said channels, line iinder means common to said channels and responsive to energy received from a channel, means controlled. over one channel for operating the first means by said line nnder and the second means by the selectively operable means, and means controlled over the other channel for operating said first means by the selectively operable means and the second means by the line finder means.

12. A system for interconnecting two channels according to claim 11, and in which said first and second means are vacuum tubes having cathodes, anodes, control grids and suppressor grids.

13. A telephone system for interconnecting calling with called channels of diierent time displacement for two-way speech over said channels, comprising a speech input tube for receiving energy from the calling and called channel, a speech output tube for applying energy to the calling and called channel, a connection for operating the output tube in accordance with the operation of the input tube, selectively operable means common to said channels for producing a time displacement of the energy received from one channel equal to the difference in time displacement between said calling and called channels, line nder means common to said channels and responsive to energy received from a channel, and means jointly controlled by said line finder and selectively operable means for alternately rendering effective said input and output means.

14. In a telephone exchange system, a cathode ray tube having a control grid and a plurality of electrodes adapted for successive engagement by the beam, a telephone line connected with each electrode, a speech input and a speech output gate tube, a connection for operating the control grid of the cathode ray tube by the output gate tube, a connection for controlling the operation of the input gate tube through the electrodes of the calling and the ycalled line, cu-toff control means for the input and the output gate tubes, means controlled by energy applied to the electrodes for controlling said cut-off control means, means controlled by the input gate 15. In a telephone exchange system, a cathode ray tube having a control grid and a plurality of electrodes adapted for successive engagement by the beam, a telephone line connected with each electrode, a speech input and a speech output gate tube each having a cathode, an anode, a control grid and a suppressor grid, a connection from the control grid of the cathode ray tube to the anode of the output gate tube, a connection for applying potentials to the control grid of the input gate tube through the electrodes of the calling and the called line, two triodes, one for applying potentials to the suppressor grid of the input and the other for applying potentials to the suppressor grid of the output gate tube, a line nder gate tube controlled by energy applied to the electrodes, a multiple connection from the output of the line nder gate tube to the grids of said triodes, a connection from the plate of the input to the control grid of the output gate tube, a low pass lter in the last-mentioned connection, a line selecting circuit variably operable in accordance with the designation of the called line, and means operable upon the actuation of the line selecting circuit for applying a potential to the multiple connection to the grids of the triodes.

16. In a telephone exchange system, a cathode ray tube having a control grid and a plurality of dynodes, means for continuously rotating the beam of said tube successively to engage said dynodes, a telephone line connected with each dynode, a speech input and a speech output gate tube each having a cathode, an anode, a control grid and a suppressor grid, a connection from the control grid of the cathode ray tube to the anode of the output gate tube, gain control means in said connection to keep the total gain around the system at less than unity, a connection for applying potentials to the control grid of the input gate tube through the dynodes of the calling and the called line, two triodes, one for applying potentials to the suppressor grid of the input and the other for applying potentials to the suppressor grid of the output gate tube, a line iinder gate tube controlled by energy applied to the dynodes, a multiple connection from the output of the line finder gate tube to the grids of said triodes, a connection from the plate of the input to the control grid of the output gate tube, a low pass filter in the last-mentioned connection, a line selecting circuit comprising register and counter tubes variably operable in accordance with the designation of the called line, time channel gate tubes controlled by the counters, and means operable upon the actuation of any time channel gate tube for applying a potential to the multiple connection to the grids of the triodes.

DAVID I-I. RANSOM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,057,773 Finch Oct. 20, 1936 2,185,693 Mertz Jan. 2, 1940 2,263,369 Skillman Nov. 18, 1941 2,265,216 Wolf Dec. 9, 1941 2,277,192 Wilson Mar. 24, 1942 2,387,018 Hartley Oct. 16, 1945 2,406,165 Schroeder Aug. 20, 1946 

